Dissecting the autoantibody repertoire in CASPR2-antibody encephalitis

Autoantibodies to contactin-associated protein 2 (CASPR2) are found in patients with an immunothe- rapy-responsive encephalitis, and show a strong HLA-DRB1*11:01 restriction. However, no studies have focussed on how the autoreactive B cells are produced and perpetuate longitudinal autoantibody production. This question has therapeutic implications.To isolate B-cells reactive to CASPR2, we cultured naïve and memory B-cells from two CASPR2-antibody encephalitis patients and two healthy donors with screening for CASPR2-reactivity on live-cell based assays. CASPR2-reactive immunoglobulins were cloned and recombinantly expressed as monoclonal antibodies (mAbs). Naïve B-cell CASPR2-reactivity was detected in both patients and healthy donors, both at a frequency of ~ 1/250 B cells. However, memory B-cell CASPR2-reactivity was exclusive to patients at a frequency of ~1/250. CASPR2-specific mAbs showed discrete domain-specificities between the antigen-specific naïve and memory B-cell derived clones. Furthermore, only memory B-cell-derived CASPR2-specific mAbs were able to bind live rat hippocampal neurons and induce internalisation of surface CASPR2.In summary, we show that early B-cell tolerance against the neuronal antigen CASPR2 is not counter-se- lected in health; however, only patients have CASPR2-specific memory B-cells, suggesting that late B-cell tolerance dysfunction may have a key role in disease pathogenesis.bo.sun@ndcn.ox.ac.uk